A variety of substances, such as therapeutic agents, may be delivered by inhalation, including aerosolized liquids and powder drugs, for the therapeutic treatment of the lungs and inhalation passageways and/or for the delivery of systemic agents. The inhalation of systemic therapeutic agents is considered a potential alternative to injections and other types of drug delivery systems. For example, insulin may be delivered by inhalation in aerosolized form, thus avoiding the need for the injection of insulin into a patient.
Inhaling aerosols, however, typically lacks the accuracy of injections, and so may be inappropriate for use in situations where accurate dosing is critical. With aerosolized drugs, the proper amount required for delivery is often not properly metered for delivery. For example, asthma inhalers typically have an acceptable accuracy of plus or minus 25% of the nominal dose. For systemic drug delivery of insulin, on the other hand, such a level of accuracy is considered too unpredictable to allow for appropriate use, even though aerosolized delivery may be preferable to intravenous delivery for a variety of reasons.
Thus, a need exists for accurately and predictably delivering a predetermined dose of aerosolized drugs.